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## Home the Unit

Type of Operation area showing the Home the Unit option

Some wrist devices, such as the Renishaw PHS, do not have predefined zero positions and use potentiometers instead of scales to position the wrist. These types of wrist devices need to have the zero redefined every time power to the probe head controller is interrupted. To redefine the wrist zero position, you may choose the Calibrate the Unit option (For information see the "Tip Calibration" topic discussed in this chapter) or the Home the Unit option.

Selecting Home the Unit calculates the angular error offset from the previously calculated wrist zero position by qualifying one or more probe angles on a previously calibrated sphere position. The advantage of this is you can use a minimum of one probe tip angle thereby making the process much faster than a wrist calibration.

Since PC-DMIS averages the errors of the homing procedure to provide a more accurate adjustment to the wrist error map, you use more than one probe angle to accomplish the Home the Unit operation.

To perform a Home the Unit operation:

1. Access the Probe Utilities dialog box by selecting the Insert | Hardware Definition | Probe menu option.

2. Select the same probe file that was used to calibrate the unit.

3. From the Active Tip list, select the angles you wish to use for the calibration check

4. Click the Measure button to open the Measure Probe dialog box.

5. Provide the parameters you wish to use during the calibration check. Also select the same calibration tool used during the Calibrate the Unit operation.

6. From the Type of Operation area, select the Home the Unit option.

7. Click the Measure button.

After calibrating the unit and prior to homing the unit, do not move the calibration sphere. If it is moved, you must re-calibrate the unit (for information on calibrating the unit, see the "Tip Calibration" topic in this chapter).